(a) Field of the Invention
The present invention relates to an automatic shift control device for an electronic pneumatic shift system and a method for controlling the same. More particularly, the present invention relates to an automatic shift control device for an electronic pneumatic shift system and a method for controlling the same in which a linear variable distance transducer (LVDT) is used to reduce shift shock.
(b) Description of the Related Art
In trucks, buses and other such vehicles in which an engine is provided at a rear of the vehicle, since a transmission is positioned at a substantial distance from the driver, it is necessary that there is provided a shift device which precisely, smoothly and easily conveys the operation of a clutch and a gearshift lever by the driver to the transmission. A pneumatic shift system is often used instead of the conventional hydraulic or mechanical shift system. In the pneumatic shift system, air pressure is electronically controlled to ultimately change shift modes of the transmission.
FIG. 1 shows a schematic diagram of a general electronic pneumatic shift system to which the present invention is applied.
In the general electronic pneumatic shift system, a lever position sensor 6 detects an operation of a gearshift lever 4L by the driver. The lever position sensor 6 outputs electrical signals corresponding to a changing position of the shift lever 4L to an electronic control unit (ECU) 8, and the ECU 8 outputs signals to control opened and closed states of a magnetic valve assembly 10 according to the signals received from the lever position sensor 6. Accordingly, air is supplied to or exhausted from a shift control device 12 to control a transmission 14 into various forward and reverse shift modes.
The magnetic valve assembly 10 is connected to an air tank 15 and receives the supply of air from the air tank 15. Also, by the supply and exhaust of air from and to the air tank 15 via a reaction valve 18, which is a 3-way magnetic valve connected to a reaction cylinder (not shown), a shift feeling is provided to the driver when the gearshift lever 4L is manipulated to different shift modes.
The ECU 8 is connected to a shift mode display 20, and the ECU 8 performs control such that the shift mode display 20 displays the present shift mode after receiving signals from the lever position sensor 6. The ECU 8 is also connected to a warning lamp 24 which alerts the driver either of either shift failure caused by the incorrect supply of air to the magnetic valve assembly 10, or of the mis-operation of the gearshift lever 4L by the driver. The ECU 8 detects such problems through its connection with a shift mode sensor 22.
The shift control device 12 includes a cylinder MVA 26 and a cylinder MVB 28. Air is supplied to and exhausted from the cylinder MVA 26 and the cylinder MVB 28 by the operation of the magnetic valve assembly 10 which operates according to signals output from the ECU 8. A shift rod 30 is slidably disposed in the shift control device 12. The shift rod 30 is displaced in a rightward or leftward direction (in the drawing) according to the supply of air to the cylinder MVA 26 and the cylinder MVB 28.
A striker 32 is fixedly disposed on the shift rod 30. With this configuration, when the shift rod 30 is displaced in the leftward direction, the striker 32 is also moved such that it operates the transmission 14 to either a first, third or fifth speed of a drive D range; and when the shift rod 30 is displaced in the rightward direction, the striker is moved such that it operates the transmission 14 to either a second or fourth speed of the drive D range, or into reverse. That is, when the driver operates the gearshift lever 4L to different shift modes, the ECU 8 controls the magnetic valve assembly 10 so that air is supplied to or exhausted from the cylinder MVA 26 and the cylinder MVB 28 of the shift control device 12, thereby controlling the displacement of the shift rod 30 and the striker 32.
Also, provided on one end of the shift rod 30 is a magnet 34. Magnet sensors 36 are mounted in the shift control device 12 corresponding to a position of the magnet 34. Accordingly, the magnet sensors 36 are able to detect the changing position of the magnet 34 as the shift rod 30 is displaced.
However, in the general pneumatic shift system as described above, since air pressure is used to shift the transmission 14 into different shift modes, in the case where air is abruptly supplied to the shift control device 12, the shift rod 30 and striker 32 are moved at a substantial speed such that abrupt force is applied to a synchronizer, shift fork, etc. of the transmission 14. This results in the wear of the transmission 14, as well as a reduction in shift and ride quality caused by shift shock.